In general, a fuel cell comprises a cell on which an air electrode layer, an electrolyte layer and a fuel electrode layer are laminated, a fuel-supplying part for supplying fuel as a reducing agent to the fuel electrode layer and an air-supplying part for supplying air as an oxidizing agent to the air electrode layer, and it is an electric cell in which electrochemical reaction takes place between fuel and oxygen in the air in the cell to provide an electric power to the outside. Fuel cells of various types are developed.
In recent years, because of a rise in consciousness to environmental problems and energy saving, it is studied to use a fuel cell as a clean energy source for various uses. In particular, attentions are paid to fuel cells which can generate an electric power by only supplying directly a liquid fuel comprising methanol and water (refer to, for example, patent documents 1 and 2).
Among them, liquid fuel type fuel cells making use of capillary force for supplying a liquid fuel are known (refer to, for example, patent documents 3 and 4).
Liquid fuel type fuel cells described in the above respective patent documents supply a liquid fuel from a fuel tank to a fuel electrode by virtue of capillary force, and therefore they do not require a pump for sending a liquid fuel with pressure, so that they have merits in reducing a size.
However, such liquid fuel type fuel cells as merely making use of capillary force of a porous body and/or a fiber bundle disposed in a fuel reservoir are suited to reduction in a size in terms of constitution, but because fuel is supplied directly to a fuel electrode in the form of liquid, the fuel follows imperfectly during use over a long period of time under a use situation in which it is mounted in a small-sized portable appliances and in which the direction of a cell part is changed very often in every direction, and the trouble that the fuel is cut off from being supplied is brought about, so that it is difficult to supply constantly the fuel to the fuel electrode.
On the other hand, known as one of countermeasures for solving the above defects is a fuel cell system in which a liquid fuel is introduced into a cell by virtue of capillary force and in which the liquid fuel is then vaporized in a fuel-vaporizing layer and used (refer to, for example, patent document 5). However, it has the problem that poor followability of the fuel which is a fundamental problem is not improved, and involved therein is the problem that it is difficult to reduce a size of the fuel cell having the above structure because of a system in which a liquid is vaporized and then used as fuel.
As described above, in conventional fuel reservoirs for fuel cells, the existing situation is that a liquid fuel is instably supplied in supplying the fuel directly to a fuel electrode to cause fluctuation in an output value during operation and that it is difficult to reduce a size thereof to such an extent that they can be mounted in portable appliances while maintaining stable characteristics.    Patent document 1: Japanese Patent Application Laid-Open No. 258760/1993 (claims, examples and others)    Patent document 2: Japanese Patent Application Laid-Open No. 307970/1993 (claims, examples and others)    Patent document 3: Japanese Patent Application Laid-Open No. 66066/1984 (claims, examples and others)    Patent document 4: Japanese Patent Application Laid-Open No. 188008/1994 (claims, examples and others)    Patent document 5: Japanese Patent Application Laid-Open No. 102069/2001 (claims, examples and others)